1. Field of the Invention
The present invention relates to an in-plane switching liquid crystal display (IPS LCD).
2. Description of Prior Art
A conventional liquid crystal display which employs twisted nematic control of liquid crystal molecules is burdened with the inherent problem of a narrow viewing angle. In order to overcome this problem, IPS liquid crystal displays have been developed. In such LCDs, an electric field applied to the liquid crystal molecules is generated in a plane parallel to a main substrate of the LCD.
FIG. 4 is a schematic, side cross-sectional view of a conventional IPS liquid crystal display 1. FIG. 5 is a top elevation of the LCD 1 corresponding to FIG. 4. As illustrated, the LCD 1 comprises a color filter substrate 10, a TFT (thin film transistor) substrate 12, a liquid crystal layer 14 interposed between the substrates 10, 12, and spacers 20 disposed between the substrates 10, 12 for supporting the LCD 1 and maintaining the space between the substrates 10, 12. A plurality of data lines 11 and gate lines 13 is formed on the TFT substrate 12 in longitudinal and transverse directions respectively, and the data and gate lines 11, 13 cooperatively form a plurality of pixel units arranged in a matrix. A plurality of common electrodes 17 and pixel electrodes 18 each having comb-shaped parts is formed on the TFT substrate 12. Arrow Z shows an upward direction perpendicular to the TFT substrate 12.
Referring to FIG. 6, in operation, when a voltage is applied to the common electrodes 17 and pixel electrodes 18, an electric field parallel to the color filter substrate 10 and the TFT substrate 12 is generated therebetween. Liquid crystal molecules in the liquid crystal layer 14 are oriented in accordance with the electric field to provide bright illumination for the LCD 1.
However, the electric field in the liquid crystal layer is not an ideal parallel electric field. Rather, it is arch-shaped, and decreases in strength along direction Z. Even liquid crystal molecules that are equidistant from the TFT substrate 12 are driven by a varying electric field, such that these liquid crystal molecules have different orientations relative to each other. This variation in orientations reduces the clarity of the display of the LCD 1; that is, the picture quality is lowered. In addition, liquid crystal molecules far from the TFT substrate 12 are driven by weaker portions of the electric field than those near the TFT substrate 12. Accordingly, to obtain an electric field strong enough to drive all the liquid crystal molecules, the LCD 1 needs a high driving voltage and/or small spaces between adjacent common and pixel electrodes 17, 18. This results in high power consumption and/or a low aperture ratio.
It is desired to provide an IPS liquid crystal display which overcomes the above-described deficiencies.